Electrochemical fuel cell systems are being developed for use as power supplies in a number of applications, such as automobiles, stationary power plants, and other applications. Fuel cells convert reactants (fuel and oxidant) to generate electric power and reaction products (such as water). Such fuel cell systems offer the promise of energy that is essentially pollution free, unlike conventional energy sources such as fossil fuel burning thermal power plants, nuclear reactors, and hydroelectric plants that all raise environmental issues.
In an example implementation, an alternating current (AC) electric machine may be coupled to a direct current (DC) system via a power inverter. When the AC electrical machine is operated as a motor of a vehicle, for instance, the inverter provides power to the AC electric machine by inverting DC power (received from fuel cells or other type of DC power supply, such as solar cells) into AC power, and delivers the AC power to the AC electric machine.
A DC side of the inverter may be coupled to a high voltage (HV) DC bus. Other components are also typically coupled to the HVDC bus, including the fuel cells or other DC power source. The inverter can comprise a plurality of switches, such as six insulated gate bipolar transistors (IGBTs) that comprise pairs of switches for a 3-phase inverter, with a system controller controlling the switching of the transistors and other associated operations of the power system. An example embodiment of an inverter is described in U.S. Pat. No. 6,927,988, entitled “METHOD AND APPARATUS FOR MEASURING FAULT DIAGNOSTICS ON INSULATED GATE BIPOLAR TRANSISTOR CONVERTER CIRCUITS,” assigned to the same assignee as the present application, and incorporated herein by reference in its entirety.
A house keeping power supply (HKPS) may be used to provide power and/or electrical signals to the system controller and/or other functional units. In DC implementations, the DC power output from the HKPS is provided to the system controller and to individual electrical functional units of the vehicle through a DC bus. The DC power output of the HKPS is then locally converted to different DC voltage levels as needed by the system controller and/or the functional units. With this DC bus approach, multiple DC/DC converters are used. However, there are a number of drawbacks in using multiple DC/DC converters, including requirements for complex circuitry, increased costs, increased electromagnetic compatibility (EMC) issues, and decreased system reliability.
An alternative implementation is to use a HKPS with an AC bus. That is, the HKPS transforms input DC power to output AC power, and distributes the output AC power to the system controller and/or to functional units of the vehicle via an AC bus.
Failures and other malfunctions of the HKPS need to be detected. Such malfunctions can include, for example, loss of power on the AC bus, abnormally high or abnormally low voltages or current, bus disconnections, or other abnormal condition or state of the AC bus. If the malfunctions are not addressed (such as by disconnecting the HKPS from the power system), then damage to high power devices or other components in the power system may occur due to undefined states or other aggravating factor(s).